The present invention relates to an improved form of an axial split-pin tumbler type lock and key combination. Heretofore, various types of axial split-pin tumbler-type locks have been devised, the differences from one to the other relating to attempts to render the lock more pick resistant.
For example, a tamper proof axial split-pin tumbler-type lock is disclosed in U.S. Pat. No. 3,541,819, which is directed to a lock constructed to induce a "false picking" which will not operate the lock. Another example of an axial split-pin tumbler-type lock is disclosed in U.S. Pat. No. 3,729,964, which employs a plurality of keys for controlling operation of the lock.
Similarly, Pat. No. 3,916,657, is again directed to an axial split-pin tumbler-type lock which is designed to operate only with a series of keys in a particular successive order thereby to render any picking operation more difficult. A first key operates to rotate both parts of a plug assembly conjointly, while the second key operates to rotate only one of the two parts, the other part being rotated to an inoperative position in which the lock cannot be picked directly. It is therefore necessary that both keys be utilized to operate the lock.
While it is known that various of the prior art axial split-pin tumbler-type locks have been devised and have achieved varying degrees of success in terms of being pick resistant, it is known that, ultimately, any lock may be picked. The goal is therefore to improve upon such types of locks in order to render the picking operation more difficult, and especially more time consuming. Insofar as picking operations are concerned, it is well-known that if one has access to the driver tumblers, especially in an axial split-pin tumbler-type lock, one can then apply a picking tool in order to move the tumblers to a point of the shear plane of the lock parts, and once that is determined, and if all tumblers are moved to the proper shear plane position, the lock may opened. Hence, the essence of a picking tool is to have access to the driver tumblers, usually from the front face of the lock.
The lock of the present invention is intended as an improvement over commonly known axially split-pin tumbler-type locks which provides an alternate means of shielding the driver tumblers from access by a picking tool via the front face of the lock.